Hair treatment compositions such as depilatory products and hair straightening and permanent waving products typically contain reducing sulphur species such as sulphides and thioglycolates, with depilatory products commonly including calcium thioglycolate and hair straightening and permanent waving products commonly including ammonium thioglycolate. The reducing sulphur species generate a variety of sulphur-containing volatiles, including hydrogen sulphide, methanethiol, dimethyl sulphide and dimethyl trisulphide, which are present at low levels in air above such products. This results in an unpleasant odour, which increases substantially during use, which can be offensive to users.
The present inventors have surprisingly found that incorporating zinc compounds, particularly zinc oxide, in such hair treatment compositions substantially reduces malodour production, both on storage and in use.